title: Evolution of highly pathogenic H5N1 avian influenza viruses in Vietnam between 2001 and 2007.
abstract: Highly pathogenic avian influenza (HPAI) H5N1 viruses have caused dramatic economic losses to the poultry industry of Vietnam and continue to pose a serious threat to public health. As of June 2008, Vietnam had reported nearly one third of worldwide laboratory confirmed human H5N1 infections. To better understand the emergence, spread and evolution of H5N1 in Vietnam we studied over 300 H5N1 avian influenza viruses isolated from Vietnam since their first detection in 2001. Our phylogenetic analyses indicated that six genetically distinct H5N1 viruses were introduced into Vietnam during the past seven years. The H5N1 lineage that evolved following the introduction in 2003 of the A/duck/Hong Kong/821/2002-like viruses, with clade 1 hemagglutinin (HA), continued to predominate in southern Vietnam as of May 2007. A virus with a clade 2.3.4 HA newly introduced into northern Vietnam in 2007, reassorted with pre-existing clade 1 viruses, resulting in the emergence of novel genotypes with neuraminidase (NA) and/or internal gene segments from clade 1 viruses. A total of nine distinct genotypes have been present in Vietnam since 2001, including five that were circulating in 2007. At least four of these genotypes appear to have originated in Vietnam and represent novel H5N1 viruses not reported elsewhere. Geographic and temporal analyses of H5N1 infection dynamics in poultry suggest that the majority of viruses containing new genes were first detected in northern Vietnam and subsequently spread to southern Vietnam after reassorting with pre-existing local viruses in northern Vietnam. Although the routes of entry and spread of H5N1 in Vietnam remain speculative, enhanced poultry import controls and virologic surveillance efforts may help curb the entry and spread of new HPAI viral genes.
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Xiu-Feng
authors.initials: XF
authors.lastname: Wan
authors.forename: Tung
authors.initials: T
authors.lastname: Nguyen
authors.forename: C Todd
authors.initials: CT
authors.lastname: Davis
authors.forename: Catherine B
authors.initials: CB
authors.lastname: Smith
authors.forename: Zi-Ming
authors.initials: ZM
authors.lastname: Zhao
authors.forename: Margaret
authors.initials: M
authors.lastname: Carrel
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Inui
authors.forename: Hoa T
authors.initials: HT
authors.lastname: Do
authors.forename: Duong T
authors.initials: DT
authors.lastname: Mai
authors.forename: Samadhan
authors.initials: S
authors.lastname: Jadhao
authors.forename: Amanda
authors.initials: A
authors.lastname: Balish
authors.forename: Bo
authors.initials: B
authors.lastname: Shu
authors.forename: Feng
authors.initials: F
authors.lastname: Luo
authors.forename: Michael
authors.initials: M
authors.lastname: Emch
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Matsuoka
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Lindstrom
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Cox
authors.forename: Cam V
authors.initials: CV
authors.lastname: Nguyen
authors.forename: Alexander
authors.initials: A
authors.lastname: Klimov
authors.forename: Ruben O
authors.initials: RO
authors.lastname: Donis
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005814:Genes, Viral; D005838:Genotype; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D005585:Influenza in Birds / Q000635:transmission / Q000821:virology*; D007251:Influenza, Human; D011200:Poultry; D011201:Poultry Diseases / Q000635:transmission / Q000821:virology; D019371:Topography, Medical; D014744:Vietnam; D014774:Virulence / Q000235:genetics